1. Field of the Invention
The present invention relates to building construction supports, and more particularly, to an elevated base for supporting a wood column and protecting the column lowermost portion from rot and other deterioration due to exposure to moisture, heat, fungus, and parasites such as wood-boring insects.
2. Description of the Related Art
Wood has been a traditional material in the world's tropic and two temperate zones, especially where lumber is an indigenous product which is easily available locally. But in tropical regions such as Central and South America, Africa, and Southeast Asia, wooden structures are susceptible to deterioration from the effects of humidity, heat and ultraviolet radiation. Usually the lowermost portion (i.e., the base portion) of vertical wood columns which support a building is the most vulnerable structural element because it is most exposed to moisture. In buildings having side walls as in the temperate zones, water accumulates through seepage; in buildings on stilts as in the tropics, support column base portions are directly exposed repeatedly as rain water accumulates and evaporates. Therefore, the lifetime of a building depends largely upon how long its columns endure. Typically, the life of a wood column in the tropics is limited to about 20 years, with failure due to rot usually occurring where the column intersects the earth. But where rotting has been prevented, e.g., by placing a building on a solid foundation of stone, the building can last for hundreds of years. Concrete block construction is about 30-45 percent more expensive than wood construction. The cost spread depends both on the import tariff on bulk cement in a particular country and on the transportation cost of bagged cement or concrete blocks, which is particularly expensive if an oil refinery is not available for processing crude oil into gasoline for the truckers. Houses built in the tropics with concrete blocks can last about twice as long as wooden houses provided prudent construction techniques are used, e.g., coating exterior walls with stucco. In the late 1940's and 1950's, concrete blocks were extensively used. However, shoddy construction then has resulted in houses being abandoned now due to rapid deterioration. Although building practices in the tropics have been improved in recent years, particularly through the use of poured concrete instead of concrete blocks, the feasibility and affordability of new housing in a region often are largely determined not by local builders but by the concrete and trucking industries. Wood, although often in plentiful supply locally and offering the potential advantages of decentralized production and distribution by saw mills in forests and lumber yards in towns, remains a bad investment compared to concrete.
There is thus an urgent need, especially in the tropics, for a method of building houses from lumber available locally which can produce houses which will last at least as long as those built using concrete. The problems in achieving such longevity are preventing the wood support column base portion from rotting and providing a stanchion-type base to enclose and support the base portion which can withstand the high up-loads, down-loads and transverse loads to which the column would be subjected during hurricanes.
Bases to support wood and steel columns in the construction of buildings, and post bases used in the construction of wooden decks, porches and fences are known in the art. U.S. Pat. No. 5,568,909 ("'909") to R. J. Timko discloses a mounting bracket for housing a wood post installed on a flat surface. The bracket includes a square tube having four side walls and open upper and lower ends, dimensioned to receive a wood post having a nominal four inch-by-four inch ("4.times.4") cross-section. The tube lower end is attached to a square base portion having a hole at each comer to receive a concrete anchor bolt, lag bolt or wood screw. The bolts or screws secure the base plate to a concrete porch, wooden deck or flat roof. The post is secured within the tube by nails each received through a hole in a side wall and driven into the post. An aperture in one side wall extending upwardly from the lower tube end allows water that enters the tube to drain.
U.S. Pat. No. 5,456,441 ("'441") to G. Callies discloses a post base for supporting a wood post relative to a concrete footing in which a seat member which receives the wood post bottom end is rotatably adjustable relative to an anchor member embedded and immovably propositioned in a poured concrete footing. The seat member has a base and two side flanges integrally formed with and generally orthogonal to the base. The base receives the post bottom end and the flanges engage two opposed post sides. The post is secured to the seat member by nails each received through a hole in a side flange and driven into the post. The base is rotatably attached to three expanded portions of the anchor member, two of which capture the base top and bottom sides, with the third forming a collar coinciding with a center opening in the base.
U.S. Pat. No. 5,090,165 ("'165") to L. D. Kenny discloses a molded plastic sleeve (or boot) which fits over the circumferential base of a wood post or pole embedded in the ground. The plastic sleeve forms a barrier intended to retard the decaying or rotting of the wood. The base of the post or pole must be reduced to fit into an opening in the sleeve. An umbrella-like rim at the top of the sleeve deflects excess moisture which may run down the post away from the sleeve. The sleeve has two vents each covered by a molded hood, extending from the sleeve base to several inches above the ground, which provide expansion areas for freezing should moisture accumulate in the sleeve.
U.S. Pat. No. 4,972,642 ("'642") to F. P. Strobl, Jr. provides a foot for supporting a wood post at the bottom of a hole in the ground which typically extends below the frost line. The plastic foot is monolithically molded and has a dish-shaped bottom wall configured to be supported by the earth at the bottom of the hole. Radial rib structures on the bottom wall distribute loads over the entire wall.
U.S. Pat. No. 4,644,713 ('"713") to J. F. Lehman is directed to a post anchor device to rapidly position and support a post in the ground. The device has a tubular ground engaging portion with a tapered end that is driven into the ground, and a post receiving portion with an upstanding bracket into which the post is received and secured by fasteners.
U.S. Pat. No. 4,048,776 ('"776") to K. Sato discloses a steel base plate for connecting a steel column of a steel structure to a concrete foundation. The base plate is formed by molding or die-forging without welding any ribs thereto to eliminate the risk of generating welding strain. A projection extending from a planar bottom portion provides a top surface whose shape is substantially identical to the cross-section of a column to be supported by the base plate. Smoothly curved sidewall portions at the junctions between the projection and bottom portion are intended to eliminate stress concentration. Holes in the base plate allow anchor bolts to extend therethrough.
None of these references addresses the problem of protecting a wood column from deterioration while also providing support against high mechanical loading. The '909 mounting bracket is adapted for housing a wood post installed on a flat deck so that the post lower portion is well away from the bare earth. The seat member of the '441 post base is above ground but no provision is made for protecting the post lower end from the environment. The '642 plastic foot supports a wood post in a hole in the ground whose lower portion is unprotected from contact with the earth. The '165 sleeve forms a barrier which protects the base of a wood post or pole buried in the earth, but does not provide support against loading. The '713 post anchor provides neither environmental protection nor structural support. The '776 column base member has high mechanical strength and rigidity, but houses a steel column in a steel structure rather than a wood column in a wooden structure.